1. Field of the Invention
This invention relates to an antenna arrangement having plural antenna elements. More specifically, the invention relates to an array antenna particularly suitable for a pulse radar active phased array system, or the like which electronically scans during transmitting/receiving.
2. Description of the Related Art
A known array antenna arrangement is shown in FIG. 5 (PRIOR ART). This particular antenna arrangement is for an active phased array pulse radar. A signal source 51 generates high frequency carrier signals during a predetermined period of time and having a constant pulse repetition rate which are the transmitting signals. The transmitting signals are distributed to plural transmitting/receiving modules 53 (shown as modules 53-1 to 53-N in the drawings) by a distributor 52. Each of modules 53 has the same configuration. A module 53 includes a phase shifter 54, a high power amplifier 55, a duplexer 56 and a low noise amplifier 57. The phase shift of phase shifter 54 is controlled by an external phase control signal.
Operation in either a transmission mode or a reception mode is selected by a transmitting/receiving control signal which is supplied to duplexer 56 from an external source. During transmission mode operation, the phase of the transmitting signal is controlled by phase shifter 54 which provides high power amplifier 55 with an output signal. Amplified signals from respective high power amplifiers 55 are supplied to an antenna element 58s (shown as elements 58-1 to 58-N in the drawings) through respective duplexers 56 in each of transmitting/receiving modules 53. Antenna elements 58 radiate electromagnetic waves forming beam patterns in accordance with the control of the phases of the respective transmitting signals by phase shifters 54.
During reception mode operation, high frequency signals received by antenna elements 58 are supplied to low noise amplifiers 57 through duplexers 56 in transmitting/receiving modules 53. Low noise amplifiers 57 supply amplified signals to receiving modules 59 (shown in the drawings as modules 59-l to 59-N). First and second oscillators 60 and 61 generate first and second local oscillating signals L1 and L2 which are supplied to distributors 62 and 63 for high frequencies. First and second local oscillating signals L1 and L2 having different frequencies are distributed to receiving modules 59 by distributors 62 and 63. A frequency of the amplified signal from low noise amplifier 57 is converted into an intermediate frequency corresponding to the difference between the received frequency and the frequency of first local oscillating signal Ll. Also, the intermediate frequency of a converted signals is converted into a low frequency between the intermediate frequency and the frequency of second local oscillating signal L2. A low frequency signal is converted into a digital signal which is supplied to a systolic array processor 64 from each of receiving modules 59. Systolic array processor 64 processes digital signals for digital beam forming and forms defined received beam. Targets can be detected by computing received data from systolic array processor 64.
In the known apparatus, transmitting signals and local oscillating signals must be distributed by large and weighty distributors 52, 62 and 63 which are used for high frequency signals. This makes the apparatus large and weighty. Also, transmitting/receiving circuits become complicated because of many signal cables for transmitting the high frequency signals. Moreover, it is difficult to carry out phase adjustment between transmitting/receiving modules.